This invention relates generally to optical correlators, and, more particularly, to a real-time programmable joint transform optical correlator.
In recent years, the acceptance of optical correlation systems has greatly expanded because of their extreme usefulness in the processing of optical signals in, for example, any type of image processing system, optical communication system, radar system, etc. More specifically, the optical correlator can effectively compare a pair of signals (objects) and by an analysis of intensity peaks determine information with respect to these signals (objects).
In 2-D coherent optical correlation, to date, there are two commonly used techniques available; one utilizes the holographic matched filter technique and the other utilizes the joint transformation method. More particularly, the development of the joint transfer correlation technique is headed in two general directions to improve its performance. One is a two-step optical-electrical process, such that the intensity distribution of the joint Fourier transformation of two object functions can be picked up by a TV vidicom camera or by arrays of charge couple device detectors wherein the detected power spectral density is electronically processed to yield the correlation of the two object functions. The other method utilizes a spatial light modulator in the Fourier plane to read out the irradiance of the joint-Fourier transform for coherent processing.
There are numerous drawbacks associated with such prior optical correlation techniques and/or systems. Of primary importance are the drawbacks associated with the lack of acceptable real-time correlation and its inability to perform programmable correlation. Furthermore, such systems as described above are elaborate in design and rely upon the critical alignment of the matched filters incorporated therein. There have been recent attempts at real-time optical correlation, however, such correlation systems still lack programmability while the alignment of the matched filter as well as the synthesis of the filter remain an elaborate procedure.
It would therefore be highly desirable to provide a totally optical technique effective in handling a large space-bandwith image capable of performing parallel multi-image correlations. In addition, it would be desirable if such a correlation technique incorporated therein standard components capable of being designed for use within a compact portable system for real-time programmable correlation.